1. Field of the Invention
The present invention relates to an image pickup apparatus including drive/control means operated in an all-pixel read mode for reading pixel signals from all pixels and a thinning read mode for reading pixel signals from all pixels in a thinned-out fashion, and more particularly to an image pickup apparatus capable of being smoothly switched over in operation between the thinning read mode and the all-pixel read mode.
2. Description of the Related Art
Recently, with image pickup apparatus using CCD image pickup devices, which are utilized in electronic cameras or the like, constructed of a large number of pixels, the apparatus has been designed to read pixels in a skipping fashion, i.e., in a thinned-out fashion, without reading all the pixels except recording of a still picture, for thereby achieving high-speed processing that is required, e.g., when an image is to be displayed in a liquid crystal display unit, and when the AE or AF operation is to be carried out. By operating the image pickup apparatus in such a thinning read mode, pixel signals can be read at a higher speed than an all-pixel read mode because all the pixels are not read in the thinning read mode. In the liquid crystal display unit, for example, the number of frames displayed per second can be increased, and therefore a smooth motion picture can be displayed rather than an intermittent frame picture.
When a CCD image pickup device is driven in the skipping read mode (thinning read mode), some of pixel lines are read, but the remaining pixel lines are not read. Then, if exposure is repeated many times for the pixel lines which are not read, signal electric charges may overflow from photodiodes constituting pixels of those lines and may mix into transfer lines. Also, in image pickup apparatus operated in the skipping read mode and the all-pixel read mode, when the operating mode is shifted from the skipping read mode to the all-pixel read mode, there arises a similar problem. Specifically, if signal electric charges overflow in some lines which are subjected to multiple exposures in the skipping read mode, the signal electric charges generated in the skipping read mode and still remained in the pixels of those lines may mix in signal electric charges generated in the all-pixel read mode.
The present invention has been made with a view of solving the above-mentioned problems in the conventional image pickup apparatus including drive/control means operated in a thinning read mode and an all-pixel read mode, and a main object of the present invention is to provide an image pickup apparatus which can prevent signal electric charges from overflowing in the thinning read mode, can hence eliminate the need of interlaced scanning, and is free from flickers.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in an all-pixel read mode for transferring the signal electric charges from all the pixels of the solid state image pickup device to the vertical registers to read pixel signals, a driving function in a thinning read mode for transferring the signal electric charges from a number n (n is one or more positive integer) of pixels for each unit of a number m (m is two or more positive integer) of pixels in the vertical direction to the vertical registers to read pixel signals, and a device shutter function for extracting the signal electric charges from each pixel to control a photoelectric conversion time, the control means being designed in the thinning read mode to carry out the operation of extracting the signal electric charges from each pixel one or more times for each read period of one frame.
By carrying out the operation of extracting the signal electric charges from each pixel one or more times for each read period of one frame when the solid state image pickup device is driven in the thinning read mode, it is possible to prevent overflow of signal electric charges from the pixels, from which the signal electric charges are not read, the overflow being otherwise caused during the operation in the thinning read mode. There can be thus provided an image pickup apparatus in which even when the same pixels are read repetitively during the operation in the thinning read mode, overflow of signal electric charges from the pixels which are not read can be prevented; hence interlaced scanning is no longer needed and the occurrence of flickers is avoided.
Another object of the present invention is to provide an image pickup apparatus which can prevent, at the time of shift from the thinning read mode to the all-pixel read mode, the signal electric charges remained in the thinning read mode from mixing in the all-pixel read mode.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in an all-pixel read mode for transferring the signal electric charges from all the pixels of the solid state image pickup device to the vertical registers to read pixel signals, a driving function in a thinning read mode for transferring the signal electric charges from a number n (n is one or more positive integer) of pixels for each unit of a number m (m is two or more positive integer) of pixels in the vertical direction to the vertical registers to read pixel signals, and a device shutter function for extracting the signal electric charges from each pixel to control a photoelectric conversion time, the control means being designed to carry out the operation of extracting the signal electric charges from each pixel one or more times immediately before the start of exposure when the solid state image pickup device is driven in the all-pixel read mode directly subsequent to the thinning read mode.
By carrying out the operation of extracting the signal electric charges from each pixel one or more times immediately before the start of exposure of the all-pixel read mode when the solid state image pickup device its shifted in operation from the thinning read mode to the all-pixel read mode, there can be provided an image pickup apparatus in which signal electric charges accumulated in the pixels, which are not read, due to multiple exposures during the thinning read mode are surely purged out and prevented from mixing in the all-pixel read mode.
Also, according to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in an all-pixel read mode for transferring the signal electric charges from all the pixels of the solid state image pickup device to the vertical registers to read pixel signals, a driving function in a thinning read mode for transferring the signal electric charges from a number n (n is one or more positive integer) of pixels for each unit of a number m (m is two or more positive integer) of pixels in the vertical direction to the vertical registers to read pixel signals, and a device shutter function for extracting the signal electric charges from each pixel to control a photoelectric conversion time, the control means being designed to transfer the signal electric charges from all the pixels to the vertical registers at the beginning of the read period of one frame immediately before starting to read the pixel signals of all the pixels when the solid state image pickup device is driven in the all-pixel read mode directly subsequent to the thinning read mode.
By transferring the signal electric charges from all the pixels to the vertical registers at the beginning of the read period of one frame immediately before starting to read the pixel signals of all the pixels when the solid state image pickup device is shifted in operation from the thinning read mode to the all-pixel read mode, there can be provided an image pickup apparatus in which signal electric charges are cleared up from all the pixels, allowing the exposure to start from an empty state, and therefore signal electric charges accumulated due to multiple exposures during the thinning read mode are surely prevented from mixing in the all-pixel read mode.
Still another object of the present invention is to provide an image pickup apparatus which can prevent, at the time of shift from the thinning read mode to the all-pixel read mode, the signal electric charges remained in the thinning read mode from mixing in the all-pixel read mode, and which can also remove smear components leaking into the registers at the same time.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in an all-pixel read mode for transferring the signal electric charges from all the pixels of the solid state image pickup device to the vertical registers to read pixel signals, a driving function in a thinning read mode for transferring the signal electric charges from a number n (n is one or more positive integer) of pixels for each unit of a number m (m is two or more positive integer) of pixels in the vertical direction to the vertical registers to read pixel signals, and a device shutter function for extracting the signal electric charges from each pixel to control a photoelectric conversion time, the control means being designed to transfer the signal electric charges from all the pixels to the vertical registers and then transfer the signal electric charges in the vertical registers at a high speed immediately before starting to read the pixel signals of all the pixels when the solid state image pickup device is driven in the all-pixel read mode directly subsequent to the thinning read mode.
By transferring the signal electric charges from all the pixels to the vertical registers immediately before starting to read the pixel signals of all the pixels when the solid state image pickup device is shifted in operation from the thinning read mode to the all-pixel read mode, signal electric charges are cleared up from all the pixels, allowing the exposure to start from an empty state, and therefore signal electric charges accumulated due to multiple exposures during the thinning read mode are surely prevented from mixing in the all-pixel read mode. In addition, by transferring the signal electric charges, which have been transferred to the vertical registers, at a high speed for purge-out, smear components leaking into the registers can be removed at the same time.
Still another object of the present invention is to provide an image pickup apparatus which can reduce an amount of electric power consumed in the operation of extracting signal electric charges from each pixel for the device shutter function, while the operation of extracting signal electric charges from each pixel is surely achieved.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a device shutter function for extracting signal electric charges from each pixel to control a photoelectric conversion time, and performs the operation of extracting the signal electric charges from each pixel a number n (n is one or more positive integer) time(s) immediately before the start of exposure.
Hitherto, in a device shutter employed for outputting a motion picture in image pickup apparatus (the term xe2x80x9cdevice shutterxe2x80x9d means a function of variably setting a time during which electric charges are generated upon irradiation of light and accumulated in a photodiode constituting each pixel, and providing similar advantages as those obtained by opening and closing a mechanical shutter without needing any movable parts), the operation of extracting signal electric charged from the pixel has been performed by outputting a charge extracting pulse continuously from the beginning of one frame to the time immediately before the start of an exposure period in the same frame. Because the charge extracting pulse is output continuously from the beginning of one frame to the time immediately before the start of the exposure period in the same frame, a large amount of electric power is consumed. In contrast, with the present invention, by performing the operation of extracting the signal electric charges from each pixel a number n time(s) immediately before the start of exposure, the large amount of electric power consumed can be reduced. Also, by performing the operation of extracting the signal electric charges from each pixel a number n time(s) immediately before the start of exposure, the signal electric charges can be surely purged out before the start of exposure. Further, the exposure period is not affected by performing the charge extracting operation in such a manner because the exposure period is given by a period from the time at which the charge extracting operation is ended to the time at which the accumulated signal electric charges are transferred to the vertical register.
Still another object, of the present invention is to provide an image pickup apparatus which can prevent signal electric charges from overflowing into the charge transfer line even if excessively strong light enters the photodiode, and which can produce a satisfactory still picture free from noises.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of pixels constituted by photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical register for receiving signal electric charges of each pixel, and transferring the signal electric charges in the vertical direction, and a horizontal register for transferring the signal electric charges in the vertical register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a device shutter function for extracting signal electric charges from each pixel to control a photoelectric conversion time, performs the operation of extracting the signal electric charges from each pixel a number n (n is one or more positive integer) time(s) immediately before the start of exposure during a read period in which an output of the solid state image pickup device is used to form a motion picture, and performs the operation of extracting the signal electric charges from each pixel repeatedly to inhibit an exposure operation during a read period in which the output of the solid state image pickup device is used to form a still picture.
If the read period in which the output of the solid state image pickup device is used to form a still picture includes a period in which the operation of extracting the signal electric charged from the pixel is performed and a period in which that operation is not performed, noises occur at the switching point between both the periods and a horizontal streak appears in the still picture. In contrast, with the present invention, by performing the operation of extracting the signal electric charges from the pixel repeatedly to inhibit the exposure operation during the read period in which the output of the solid state image pickup device is used to form a still picture, it is possible to prevent the occurrence of noises and hence the occurrence of a horizontal streak. Also, when the operation of extracting the signal electric charges is switched over, the supply voltage is greatly varied at the switching point and a horizontal streak appears due to a corresponding step difference in brightness because the charge extracting pulse has a high voltage. With the present invention, by continuously performing the operation of extracting the signal electric charges, the supply voltage is not varied during the period in which the device output is used to form a still picture, and therefore a satisfactory still picture output can be produced.